1. Field of the Invention
The present invention relates generally to the stabilization, handling, transport, and storage of small radioactive particles removed from a volume of water. In particular, the present invention relates to a system and method of filling, dewatering, sealing and handling high integrity containers for storing high level radioactive debris filtered from a volume of water for disposal.
2. Description of the Related Art
Commercial nuclear reactor power plants have various water volumes that are subject to contamination with radioactive debris particulate. These water volumes include, for example, the refueling cavity and the spent fuel pool. The particulate contained in these water volumes typically includes xe2x80x9ccrudxe2x80x9d (corrosion products) and xe2x80x9ccutting finesxe2x80x9d that may range in size from sub-micron to several millimeters in cross-section. The cutting fines are often mixed with other non-radioactive particles that are byproducts of a cutting operation, such as abrasive or electrode materials.
There are several reasons that the radioactive debris particulate needs to be removed from the various water volumes in the nuclear reactor power plants from time-to-time. For example, the small particles often must be removed from the water for disposal, to improve water clarity, and/or to reduce the radiation level of the water volume. Once the small radioactive particles are removed from the water using a suitable filtration system, the particles must be placed in containers that allow safe handling, transport and storage of the particles.
Small, highly radioactive debris particulate, such as that generated during the dismantling of reactor internals, is considered unstable unless it is captured in high integrity containers. Conventional systems for containing the debris particulate mix or encapsulate the debris particulate with or within other materials to stabilize the material. However, the particulate stabilized in this manner is difficult to retrieve for future processing. Other conventional systems lack sufficient seals and redundancy to assure that there is no possibility of small particles migrating from the container into the water pool or other storage facility. These conventional systems also lack an integral dewatering filter, thereby making them more difficult to use and increasing the amount of secondary waste and radiation dose to operating personnel.
Vendors performing dismantling operations in the commercial nuclear power decommissioning business have experienced significant problems with refueling cavity contamination, increased costs for disposal of waste, and dose rates to personnel that are not As Low As is Reasonably Achievable (xe2x80x9cALARAxe2x80x9d). These problems have been partly due to the lack of a system for filling, sealing and handling high integrity containers for storing the concentrated radioactive particles removed from the various water volumes in the nuclear power plant.
It is an object of the present invention to provide an improved system and method of filling, sealing and handling high integrity containers for storing radioactive debris that solves the problems associated with the prior art.
It is a further object of the present invention to provide an improved system and method of remotely filling, dewatering, sealing and handling high integrity containers underwater for storing radioactive debris to minimize radiation exposure to operating personnel.
It is a further object of the present invention to provide a system and method of filling and dewatering high integrity containers using a vibration source to assist flow through an internal filter during a dewatering process.
It is a still further object of the present invention to provide a system for filling, sealing and handling high integrity containers using a plurality of valves for isolating fill and dewatering lines to assure minimal release of particulate during connector mating and demating operations.
According to the present invention, an improved system is provided for filling, dewatering and sealing high integrity containers for storing high level radioactive debris. The system has a support structure for receiving a container and a movable hood supported over the support structure. The movable hood is movable between a filling/dewatering position, an intermediate position, and a sealing position. Fill and dewatering lines extend through the hood and have flexible lower portions with connectors for interfacing with the container to be filled. The flexible lower portions are movable into and out of engagement with respective connectors on the container when the hood is in the filling/dewatering position. A plurality of valves are provided to isolate the fill and dewatering lines to minimize release of radioactive debris during connector mating and demating operations. A straw extends through the hood for removing water from an upper volume of the container when the hood is in the intermediate position. A closing structure is supported by the hood for lowering a cover into engagement with the container and fastening the cover to the container when the hood is in the sealing position. A vent line is provided for purging gas from the hood. A vibrator is positioned within the support structure for engaging and vibrating the container to facilitate filling and dewatering operations. A scale is positioned between the container and the support structure for determining when the container is full.
According to another broad aspect of the present invention, a combination of a container for storing radioactive debris and a system for filling and sealing the container is provided. The container comprises an enclosure having a primary volume for receiving and containing radioactive debris; a fill tube in fluid communication with said primary volume for injecting radioactive debris into said primary volume; a dewatering filter having a filtering surface exposed to a space for containing radioactive debris within said primary volume; and a dewatering tube in fluid communication with said dewatering filter for extracting water from said container that passes through said dewatering filter. The system for filling and sealing the container comprises a support structure having a space into which said container is received; a hood supported over said support structure, said hood being movable relative to said support structure between a filling/dewatering position and a sealing position; a fill line supported by said hood for injecting radioactive debris into said container when said hood is in said filling/dewatering position, said fill line being movable into fluid communication with said fill tube of said container; a dewatering line supported by said hood for removing water from said primary volume of the container when said hood is in said filling/dewatering position, said dewatering line being movable into fluid communication with said dewatering tube of said container; and a closing structure supported by said hood for securing a cover over the container when said hood is in said sealing position.
According to another broad aspect of the present invention, a method of filling and sealing a container with radioactive debris is provided. The method comprises the steps of: placing a container within a support structure submerged in water and covering the support structure and container with a hood submerged in the water; lowering a connector portion of a fill line into a secondary volume of the container and connecting the connector portion of the fill line to a fill tube of the container; lowering a connector portion of a dewatering line into the secondary volume of the container and connecting the connector portion of the dewatering line to a dewatering tube of the container; injecting a slurry of radioactive debris into a primary volume of the container through the fill line and fill tube; and removing fluid from the slurry of radioactive debris within the container through the dewatering tube and dewatering line.
The method according to this aspect of the present invention may also include the further steps of: vibrating the container to facilitate the removal of water from the radioactive slurry; monitoring an amount of radioactive debris within the container using a scale positioned between the support structure and the container; isolating the fill line and fill tube using a first pair of valve assemblies; isolating the dewatering line and dewatering tube using a second pair of valve assemblies; raising the respective connector portions of the fill line and dewatering line out of the secondary volume of the container; moving the hood relative to the support structure and container into an intermediate position; introducing a gas into the hood to displace water within the hood to a level below an upper end of the container; lowering a straw into the secondary volume of the container and removing water from the secondary volume through the straw; visually checking a water level in the secondary volume using a camera; raising the straw out of the secondary volume; moving the hood relative to the support structure and container into a sealing position; lowering a cover into sealing engagement with the container; and securing the cover to the container.
Numerous other objects of the present invention will be apparent to those skilled in this art from the following description wherein there is shown and described a preferred embodiment of the present invention, simply by way of illustration of one of the modes best suited to carry out the invention. As will be realized, the invention is capable of other different embodiments, and its several details are capable of modification in various obvious aspects without departing from the invention. Accordingly, the drawings and description should be regarded as illustrative in nature and not restrictive.